The lens shown in the top photograph above is a plano-convex lens whose focal characteristics model that of a gravitational lens. The shape of the lens, described in one of the reference articles in the reference list linked below, is seen in the photograph at the right.
The
experimental setup is shown in the second photograph. The distant "star" is formed by a hole in a piece of black paper or foil in front of a light source. The star can be moved by sliding it left-to-right along the optical rail behind the gravitational lens, in the same plane as the observer (video or other camera). Adjusting the height of the camera will put the observer slightly out of the plane of the motion of the star and axis of the gravitational lens. These cases are shown below.
An mpeg video shows a star passing directly behind the gravitational lens, where the star is represented by a small
disc of light. The camera, in the plane of the motion, records the light
from the star as the star passes DIRECTLY behind the gravitational lens.
The ring of light created when the distant star is EXACTLY in line with
the gravitational lens and the observer is called the Einstein
ring.
Another mpeg video shows the situation where
the distant star is slightly above the plane of the gravitational lens
and the observer.
This device was designed and produced by physicist Sid Liebes, an
expert on gravitation and relativity, and author of several of the
reference works, including both the design and application of the lens.
This additional animated video shows what one might observe when a background galaxy passes on the opposite side of a black hole from the observer.